Systems and methods for operating an RFID transponder (102). The methods involve: performing energy harvesting operations by a voltage scavenging device (130) of the RFID transponder to collect energy from an RF field, magnetic field, heat, light or movement of the RFID transponder; increasing or decreasing, by a voltage converter of the RFID transponder, a voltage level of a signal received from the voltage scavenging device to a sub-threshold voltage level that is at least one order of magnitude below a normal operating range for the RFID transponder; and supplying an operating voltage at the sub-threshold voltage level to at least a transceiver circuit (124) of the RFID transponder.